@anda_skoa: I have checked the file physically and also its timestamp also.It is indeed changing everytime.
Also I am not passing image as a parameter through my signal because I need to read the file again and again and hence I am doing it on a physical file and i know its location,so no need to pass.

@d_stranz: yes,the image processing thread is closing the file and the contents are physically written to the disk.
I think you are correct,that it is not returning to the event loop after "image finished" signal is handled..hence the UI is not updating.
Pl tell how to return to the event loop,as I am unable to do so..